Characterizing and Qualifying an LED for Automotive Exterior Signal Lamps 2002-01-0382

Light emitting diodes (LEDs) are fast becoming the light source of choice for automotive signal lamps. Before an LED can be used in an automotive signal lamp, however, a study must be made of the LEDs that are available for these applications. This is required to determine the correct LED for the particular lamp being designed. Significant parameters that must be evaluated to determine thesLED's suitability for the selected application are the wavelength of the emitted light, the radiation pattern of the light and the usable Lumen output. One additional criteria that must also be considered is the ratio of the cost per Lumen of the targeted LED. These criteria are a few of the parameters that are measured in and out of the laboratory to determine if the LED being considered can be used in an exterior automotive signal lamp application.

The selection process of the LED involves the characterization by accurately measuring the light output of the LED at a specified electrical current and thermal resistance. Once this has been completed and it has been established that the selected LED is a possible candidate for an automotive exterior signal lamp, the LED is subjected to durability performance testing. This involves testing the LED for its ability to meet the environmental, electrical and optical requirements. Since there are many manufacturers of LEDs it is necessary to choose an LED that has the highest quality along with the greatest amount of usable light output. It is this testing and characterization process that will enable us to select only the brightest and the highest quality LEDs for the automotive signal Characterization of an LED is more than the measuring the light output at a given value of input current. There are also a number of factors that must be evaluated to understand the characteristics of an LED. These factors are the radiation pattern, color of light emitted, the voltage drop across the LED, and the thermal characteristics, including thermal resistance and management.

lamp. In addition each customer has their own unique set of requirements that the light source must meet. Therefore, the light source must meet or exceed the most stringent requirements that have been set forth.